Beat beat grid go crazy when some specific files are played

[Anders Gunnarsson]

The beat grid and related graphics for cue-points etc seem to move 4-5 times the speed of the waveform when playing some specific files. These files seem to be mp3 only, where the bitrate is detected as zero or just maybe some metadata fail to load properly (See log). I can provide some test files if someone wants to debug this.

Log output related to this issue:
Debug: [Main]: BeatFactory::loadBeatsFromByteArray could not parse serialized beats.

Seen with Mixxx 1.10.0 beta1 on UbuntuStudio 11.04 64-bit.

[RJ Skerry-Ryan (rryan)]

I debugged one of the files I have that does this and it looks like TagLib is wrong about the samplerate in this case and gives 11kHz instead of 44kHz for this particular file. Judging from the TagLib code, it looks like this file has a corrupt Xing header. We do not check for Xing headers in SoundSourceMP3, so this is why the engine gets the right samplerate.

[RJ Skerry-Ryan (rryan)]

The worst part is that we store the samplerate in the database. This means that everyone out there who has loaded one of these files got the bad samplerate recorded in their database so even if we fix the code, the bug will still happen. We may need to do a 'reset the world' type of thing where we set every song samplerate to 0 in the database and then re-read detect samplerate when we load the track out of the database.

[RJ Skerry-Ryan (rryan)]

OK, after thinking about it there's no real way around these sort of problems (file corruption) so the best we can do is be consistent. The waveform and sample count is coming from libmad but the samplerate is coming from taglib. I just changed WaveformRenderBeat to use the libmad samplerate from the track_samplerate CO so at least if the waveform and beats will be consistent if they are wrong.

[Mel Grubb (melgrubb)]

I just tested this, and while the beatgrid now aligns properly with the playing track, the beatgrid itself is now very dense, as in I have 4 times as many lines as I ought to. The BPM in the database is correct, but the grid seems to be showing me every quarter note now. This is on an existing file that was exhibiting the "out of sync" problem before.

[RJ Skerry-Ryan (rryan)]

Hi Mel -- yup that bug is Bug #883661 which isn't fixed yet.

On Sat, Nov 5, 2011 at 9:39 AM, Mel Grubb <email address hidden> wrote:

> I just tested this, and while the beatgrid now aligns properly with the
> playing track, the beatgrid itself is now very dense, as in I have 4
> times as many lines as I ought to. The BPM in the database is correct,
> but the grid seems to be showing me every quarter note now. This is on
> an existing file that was exhibiting the "out of sync" problem before.
>
> --
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> https://bugs.launchpad.net/bugs/797439
>
> Title:
> Beat beat grid go crazy when some specific files are played
>
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[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/5927